Simple Research keywords: These are important to get right by culture and time period.  

• Tack: saddle, bridle, harness, armor, barding, saddle pad or blanket.
• Colors: “horse colors” or “equine color genetics”.  See Rohirrim Grey for more detail.
• Breeds and types: search according to use. Draft, fine harness or riding types, saddle horse. Distinctly different types, physical and mentally. 
• Hot blooded (more reactive) vs cold blooded.
• Gaits: walk, trot, canter or lope. Gaited breed gaits are breed specific.
• Feed types: look for locally available grains and foodstuff for historicals of any period. For example: Bedouins were known to feed camels milk and dates.

Travel Times: (see Travel Times in Middle-earth for specific examples)

• Horse walks about 3-4mph, trot about 8mph, canter/lope about 10-15mph.
• gallop up to 25-30mph, Quarter horse race horse clocked at 55mph
• Average days riding (quest) 20-30 miles per day.
• Wagons make about 15 miles, walking, with a break at midday to unhitch and rest.
• World class endurance horses running 100 miles in 7 hours.
• To add conflict and slow your hero, add difficulties on the trail such as high wind, heat, mud, deep sand, hills/mountains, rocky terrain, thick woods, rutted or pocked trails such as wagon tracks.

Stallions: If you're going to mount your hero on a stallion, have cultural or plot-based reasoning behind it and characterize the horse as a stallion rather than just using the label. Stallions are sexual creatures. They to learn to behave in socially acceptable manners, but have to be trained and managed properly. 

Mares: Can be fussy, peevish, particular, maternal, protective or jealous. They are natural leaders. They’ll accept direction and leadership if they're confident of your judgment and leadership but are likely to question speed, direction and the quality of your traveling companions.

Geldings: Are natural followers, will be your best buddy . They’re content to be taken care of and easier to maintain focus on rider/handler and the trail.

Main Peeve:  Boring horses without characterization.

Other Peeves, Misunderstandings and Misconceptions:

• Excited horses, running or in battle don't tend to show pain response to injuries until they are cooled out.
• 'Stone in the hoof' is not a crippling injury.
• Donkeys and Mules are both distinctly different than horses and from each other.
• Horse habits: busy-ness, fidgets, digs, noses
• Communicative: ears, body language
• Size: big horses require more feed and rest

Suggested Resources:

Writinghorses.com : Daily inanities, trials and tribulations of riding and raising a pocketful of horses. Real-life situations and suggestions that can be used to add depth, believability, and a little humor to your horses. (this page is no longer being updated on a regular basis, but the information is solid and a good representation of daily life with horses.)

FantasyHorseStable.com Horses for your Heroes – a virtual stable of real horses with photos, descriptions and backstory. These are real horses with personality and backstory. You can pick one that will infuriate your hero and plop her in the story.

• Donna Snyder-Smith www.DonnaSnyderSmith.com
• Linda Tellington-Jones
• Sally Swift / Centered Riding
• Note: I haven't listed some currently popular clinicians and trainers because, in my opinion, many of those programs are designed, on the surface, to help the beginner horseman learn to understand and work with the horse and some of the deeper concepts are skewed in a mechanical way that is corrected as the horsemen develop through the program.

• Horse Follow Closely by Gawani Pony Boy
• Dancing with Horses by Klaus Ferdinand Hempfling
• The Adventurists’ Mongol Derby; https://www.theadventurists.com

• Holly Lisle: especially Talyn and The Rose Sea
• Patricia Briggs: The Hob's Bargain
• Carl Raswan's Drinkers of the Wind
• L'Amour: Not just his westerns, but also in Walking Drum.
• JRR Tolkien: love & respect shown with minimal characterization